The invention relates to medical devices, and more particularly, to medical devices that deliver pacing stimuli to a heart.
A pacemaker is an electronic medical device that is used to selectively stimulate a heart with electrical pulses in order to assist the heart in circulating blood. A pacemaker may be an external device connected to the body using electrodes, but more commonly is an implanted device operating from internal batteries or via an inductive link to an external power source.
Depending upon the disease or malfunction of the heart, the pacemaker delivers pacing pulses to the atrium, the ventricles, or both, in the case of dual chamber pacemakers. By monitoring electrical activity sensed from the heart, the pacemaker determines the intrinsic rhythm of the heart, and provides stimulation pulses that force depolarization of the atrium, ventricles, or both, at appropriate times to stabilize the electrical rhythm of the heart.
Some dual chamber pacemakers are designed to avoid xe2x80x9ccompetitive atrial pacingxe2x80x9d (CAP) that may arise when the pacemaker delivers an atrial pacing pulse (AP) within the natural refractory period of the atrium. In such a situation, the atrial stimulus may either fail to achieve atrial capture, or may induce an atrial arrhythmia, including atrial fibrillation and atrial flutter. In addition, the actual interval between atrial and ventricular depolarizations of the heart will be prolonged beyond the desired AV interval. Other potential undesired effects include sustaining or even accelerating an existing atrial arrhythmia, or causing general confusion caused by the delivery of an atrial pacing pulse during an existing arrhythmia.
Consequently, some conventional dual chamber pacemakers can operate in a non-competitive atrial pacing (NCAP) mode designed to prevent competitive atrial pacing. When operating in NCAP mode, conventional pacemakers delay atrial stimuli by a pre-defined interval, referred to herein as the NCAP interval, to avoid pacing during the natural refractory period of the atrium. In some pacemakers, the interval is typically a fixed interval of, for example, 300 milliseconds. Other pacemakers support a manually adjusted interval that may be set by a clinician or other operator within a pre-determined operating range, such as between 200 milliseconds and 400 milliseconds.
Similar techniques are illustrated by Markowitz et al., U.S. Pat. No. 5,273,035, that describes a dual chamber pacing technique in which the atrial stimuli is delayed from early atrial signals to avoid atrial competition. Similarly, den Dulk, U.S. Pat. No. 5,374,280, describes a dual chamber pacemaker that identifies an early atrial sense event within a post-ventricular atrial refractory interval (PVARP), and inhibits delivery of the atrial stimuli for a predetermined interval following the occurrence of such an atrial sense event.
In general, the invention is directed to pacing techniques designed to avoid competitive atrial pacing. In particular, the techniques dynamically adjust a non-competitive atrial pacing (NCAP) interval based on sensed cardiac conditions. An apparatus capable of delivering pacing stimuli, such as a pacemaker or an implantable cardioverter/defibrillator (ICD), uses a relatively short NCAP interval under most conditions. Under other conditions, in which the atrium may be more vulnerable to initiation of atrial arrhythmia or other undesired effects, the apparatus may use a longer NCAP interval for one or more cardiac cycles.
In one embodiment, the invention provides a method comprising detecting an atrial signal during an atrial refractory period, calculating a duration based on a sensed cardiac condition, and inhibiting delivery of an atrial pacing stimulus for an interval of the calculated duration.
In another embodiment, the invention provides an apparatus comprising a pulse generator that delivers atrial pacing stimuli to a heart, and a set of sense amplifiers that produce output signals responsive to cardiac signals received from the heart. A controller calculates a duration based on the output signals of the amplifiers, and inhibits delivery of the atrial pacing stimuli for an interval of the calculated duration upon detecting an atrial signal during an atrial refractory period.
The invention offers many advantages. For example, a fixed NCAP interval having a relatively short duration, such as 300 milliseconds as used in many conventional pacemakers, may not be sufficient to prevent competitive atrial pacing and subsequent triggering of atrial arrhythmia under certain cardiac conditions. By dynamically adjusting the NCAP interval based on sensed cardiac activity, the invention reduces the risk of competitive atrial pacing under these conditions, thereby avoiding triggering atrial arrhythmia including atrial fibrillation and atrial flutter. In addition, the dynamic NCAP interval may reduce the risk of sustaining or even accelerating an existing atrial arrhythmia, and may alleviate any general confusion caused by the delivery of an atrial pacing pulse during an existing arrhythmia.
Another advantage over the prior art includes the elimination of the need for a clinician or other operator to program a fixed NCAP interval having a long duration in an attempt to avoid competitive atrial pacing. In particular, a fixed NCAP interval having a long duration tends to limit the rate at which pacing stimuli can be applied, and may also negatively impact the synchronous operation of a dual chamber pacing system. By dynamically adjusting the NCAP interval, the invention avoids such limitations.
The above summary of the invention is not intended to describe every embodiment of the invention. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.